Cleaner and more fuel efficient than fossil fuel-powered cars, electric vehicles, or EVs, are believed by many to be the automobiles of the future.

The state of California has already jumped on making this a reality, offering a rebate to those who decide to buy one. Despite the incentive, according to the DMV, only about 342,000 of California’s 30.6 million registered cars and trucks are battery-electric or plug-in hybrid EVs. But if that day comes when EVs stop being the future and become the present, how will California’s power grid withstand the strain of potentially millions of cars being plugged into charging stations across the state?

New analysis out from researchers at Lawrence Berkeley National Laboratory, a federally-funded lab that’s part of the U.S. Department of Energy, suggests that if EVs become the norm for drivers in California, the state’s power infrastructure might not be equipped to handle the strain. They say that construction of charging stations has not kept up with vehicle deployment, and while that might not be a problem now while there are relatively few on the road, it could be if demand for EVs continues to grow. They cite evening charging after drivers return from work as an area of particular concern, warning of the potential for disruption to power lines and transformers in neighborhoods where multiple homes have EVs.

How can the state prepare its power infrastructure to handle the growing number of EVs on the road that need charging? What improvements would need to be made to the grid? And how long will it be before there are enough EVs on the road to put a strain on the power grid?